There are types of medicaments that can be stored for a long time and that are filled in containers, such as cartridges, syringes, ampoules, canisters or the like, containing a ready-to-use medicament in liquid state. However, there are also other types of medicaments that are a mixture of two substances, i.e. a medicament agent (e.g. lyophilized, powdered or concentrated liquid) and a diluent (e.g. water, dextrox solution or saline solution). These types of medicaments cannot be pre-mixed and stored for a long time because the medicament agent is unstable and can be degraded and lose its effect quickly. Hence, a user, e.g. a patient himself/herself, a physician, a nurse, hospital personnel or trained persons, must perform the mixing within a limited time period prior to delivery of a dose of medicament to a patient. Further, some medicament agents are subject to chemical changes during mixing. Such sensitive medicament agents require a particular treatment when mixing with a diluent, since excessive mixing force will degrade said medicament agents.
In order to facilitate the mixing, a number of containers for mixing have been developed to comprise at least two chambers, known as multi-chamber containers. These multi-chambered containers comprise a first chamber containing the medicament agent and at least a second chamber containing the diluent. These chambers are sealed off with stoppers such/so that the medicament agents are separated from the diluent and do not become degraded. When the medicament agent is to be mixed, shortly before administering, redirecting passages are opened between the chambers, usually by depressing a distal stopper and in turn a divider stopper of the container somewhat. The passages allow the mixing of the medicament agent and the diluent to prepare the medicament for delivery.
The above mentioned requirements can be achieved by simple medicament delivery devices, such as a common hypodermic syringe, but the procedure is of course rather awkward, in particular for users who are not used to handle these devices. In order to facilitate for the patient to self-administer the medicament with a predetermined dose in an easy, safe and reliable way and also to facilitate the administration of medicaments for hospital personnel in the same facilitated way, a number of automatic and semi-automatic devices have been developed, incorporating these multiple-chamber solutions, to mix the medicament before delivery.
A self-injection device arranged with a dual-chamber container, wherein both the mixing and the injection are done automatically by mechanical means, such as springs and other means, is disclosed in U.S. Pat. No. 4,755,169. A similar solution is disclosed in U.S. Pat. No. 6,793,646 wherein the mixing of a dual-chamber cartridge is done automatically by springs upon activation of the device. The injection is done automatically by applying a forwardly-directed force to a plunger rod using the same spring as used for the mixing action. A drawback with these devices is that the mixing force, which medicament agents are subjected to, is initially very high, as described by Hooke's law. Hence, the medicament agents may be degraded.
Another solution is disclosed in WO 2004004809, wherein both the mixing and the injection are done automatically by electronically controlled means. A drawback with this device is that the electronics are dependent on batteries and are very sensitive to noise, moisture, water, etc., which can result in device malfunction. Furthermore, the manufacture of electronic devices is more expensive than the manufacture of mechanical devices.
In U.S. Pat. No. 6,319,225 the mixing of a dual-chamber ampoule is done manually. The device is pushed vertically against a surface, with its proximal end pointing upwards, causing a relative upward movement of a plunger rod and a stopper inside an ampoule, such that mixing is performed. The process is visually observable. U.S. Pat. No. 6,319,225 teaches that the most suitable process for mixing a medicament agent with a diluent, is by manually controlling the speed of the diluent flow under visual inspection. A drawback of this device is that the mixing force, which medicament agents are subjected to, can be high if the user is stressed and urgently needs to use the device. Hence, the medicament agents may be degraded.
Moreover, the handling and safety aspects of injector devices, having a certain degree of automatic functions, as well as providing immediate accessibility in emergency situations, are issues that attract a lot of attention in development of these types of devices.
Even though many of the devices on the market, as well as the ones described above, have their respective advantages, there is still room for improvements, especially improvements regarding the mixing of medicament in a safe and automatic way using components and functions that are dedicated to a mixing sequence.